Probably in old times in the time of hunger cows were more important than people. The issues probably was that people can t eat grass. From other side from cow s milk a lot of products can be done and it was much more profitable to have the cow, rather than killing it. Obviously when there were too much of people and very few of cows, cow life cost was higher. Maybe it s still higher in some regions.
The cow in India is considered a sacred animal. The cow to Hindus is equivalent to the status of the mother, because this animal has such maternal qualities as humility, kindness, wisdom and peace.
There are several legends that tell about how a cow became a sacred animal of the Hindus. And they are all very interesting.
According to Hindu mythology, the Hindu, to after death get to heaven, you must cross the river. To make it possible only with the help of the cow, holding its tail.
The Puranas (ancient sacred text of Hinduism) says that the Gods, creating the ocean, took from him a cow Kamdhenu that could grant any wish. Hindus believe that each cow is Kamdhenu and can also fulfill human desires, if it is to love and honor.
The cow is a wet nurse because milk and all dairy products are very beneficial for human health.